// For flags

CVE-2022-48845

MIPS: smp: fill in sibling and core maps earlier

Severity Score

5.5
*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

In the Linux kernel, the following vulnerability has been resolved:

MIPS: smp: fill in sibling and core maps earlier

After enabling CONFIG_SCHED_CORE (landed during 5.14 cycle),
2-core 2-thread-per-core interAptiv (CPS-driven) started emitting
the following:

[ 0.025698] CPU1 revision is: 0001a120 (MIPS interAptiv (multi))
[ 0.048183] ------------[ cut here ]------------
[ 0.048187] WARNING: CPU: 1 PID: 0 at kernel/sched/core.c:6025 sched_core_cpu_starting+0x198/0x240
[ 0.048220] Modules linked in:
[ 0.048233] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc3+ #35 b7b319f24073fd9a3c2aa7ad15fb7993eec0b26f
[ 0.048247] Stack : 817f0000 00000004 327804c8 810eb050 00000000 00000004 00000000 c314fdd1
[ 0.048278] 830cbd64 819c0000 81800000 817f0000 83070bf4 00000001 830cbd08 00000000
[ 0.048307] 00000000 00000000 815fcbc4 00000000 00000000 00000000 00000000 00000000
[ 0.048334] 00000000 00000000 00000000 00000000 817f0000 00000000 00000000 817f6f34
[ 0.048361] 817f0000 818a3c00 817f0000 00000004 00000000 00000000 4dc33260 0018c933
[ 0.048389] ...
[ 0.048396] Call Trace:
[ 0.048399] [<8105a7bc>] show_stack+0x3c/0x140
[ 0.048424] [<8131c2a0>] dump_stack_lvl+0x60/0x80
[ 0.048440] [<8108b5c0>] __warn+0xc0/0xf4
[ 0.048454] [<8108b658>] warn_slowpath_fmt+0x64/0x10c
[ 0.048467] [<810bd418>] sched_core_cpu_starting+0x198/0x240
[ 0.048483] [<810c6514>] sched_cpu_starting+0x14/0x80
[ 0.048497] [<8108c0f8>] cpuhp_invoke_callback_range+0x78/0x140
[ 0.048510] [<8108d914>] notify_cpu_starting+0x94/0x140
[ 0.048523] [<8106593c>] start_secondary+0xbc/0x280
[ 0.048539]
[ 0.048543] ---[ end trace 0000000000000000 ]---
[ 0.048636] Synchronize counters for CPU 1: done.

...for each but CPU 0/boot.
Basic debug printks right before the mentioned line say:

[ 0.048170] CPU: 1, smt_mask:

So smt_mask, which is sibling mask obviously, is empty when entering
the function.
This is critical, as sched_core_cpu_starting() calculates
core-scheduling parameters only once per CPU start, and it's crucial
to have all the parameters filled in at that moment (at least it
uses cpu_smt_mask() which in fact is `&cpu_sibling_map[cpu]` on
MIPS).

A bit of debugging led me to that set_cpu_sibling_map() performing
the actual map calculation, was being invocated after
notify_cpu_start(), and exactly the latter function starts CPU HP
callback round (sched_core_cpu_starting() is basically a CPU HP
callback).
While the flow is same on ARM64 (maps after the notifier, although
before calling set_cpu_online()), x86 started calculating sibling
maps earlier than starting the CPU HP callbacks in Linux 4.14 (see
[0] for the reference). Neither me nor my brief tests couldn't find
any potential caveats in calculating the maps right after performing
delay calibration, but the WARN splat is now gone.
The very same debug prints now yield exactly what I expected from
them:

[ 0.048433] CPU: 1, smt_mask: 0-1

[0] https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=76ce7cfe35ef

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: MIPS: smp: complete los mapas de hermanos y núcleos antes Después de habilitar CONFIG_SCHED_CORE (aterrizado durante el ciclo 5.14), se inició interAptiv de 2 núcleos y 2 subprocesos por núcleo (controlado por CPS) emitiendo lo siguiente: [0.025698] La revisión de CPU1 es: 0001a120 (MIPS interAptiv (multi)) [0.048183] ------------[ cortar aquí ]------------ [0.048187] ADVERTENCIA: CPU: 1 PID: 0 en kernel/sched/core.c:6025 sched_core_cpu_starting+0x198/0x240 [0.048220] Módulos vinculados en: [0.048233] CPU: 1 PID: 0 Comm: swapper/1 No contaminado 5.17 .0-rc3+ #35 b7b319f24073fd9a3c2aa7ad15fb7993eec0b26f [0.048247] Pila: 817f0000 00000004 327804c8 810eb050 00000000 00000004 00000000 c314fdd1 [ 0.048278] 830cbd64 819c0000 81800000 817f0000 83070bf4 00000001 830cbd08 00000000 [ 0.048307] 00000000 00000000 815fcbc 4 00000000 00000000 00000000 00000000 00000000 [ 0,048334] 00000000 00000000 00000000 00000000 817f0000 00000000 00000000 817f6f34 [ 0.048361] 817f0000 818a3c00 817f0000 00000004 00000000 00000000 4dc33260 0018c933 [ 0.048389] ... 0.048396] Seguimiento de llamadas: [ 0.048399] [&lt;8105a7bc&gt;] show_stack+0x3c/0x140 [ 0.048424] [&lt;8131c2a0&gt;] dump_stack_lvl+0x60 /0x80 [ 0.048440] [&lt;8108b5c0&gt;] __warn+0xc0/0xf4 [ 0.048454] [&lt;8108b658&gt;] warn_slowpath_fmt+0x64/0x10c [ 0.048467] [&lt;810bd418&gt;] 198/0x240 [ 0.048483] [&lt;810c6514&gt;] sched_cpu_starting +0x14/0x80 [ 0.048497] [&lt;8108c0f8&gt;] cpuhp_invoke_callback_range+0x78/0x140 [ 0.048510] [&lt;8108d914&gt;] notify_cpu_starting+0x94/0x140 [ 0.048523] [&lt;8106593c&gt;] _secundario+0xbc/0x280 [ 0,048539] [ 0,048543] - --[ end trace 0000000000000000 ]--- [ 0.048636] Sincronizar contadores para CPU 1: hecho. ...para cada uno menos CPU 0/arranque. Las impresiones de depuración básicas justo antes de la línea mencionada dicen: [0.048170] CPU: 1, smt_mask: Entonces smt_mask, que obviamente es una máscara hermana, está vacía al ingresar a la función. Esto es crítico, ya que sched_core_cpu_starting() calcula los parámetros de programación central solo una vez por inicio de CPU, y es crucial tener todos los parámetros completados en ese momento (al menos usa cpu_smt_mask() que de hecho es `&amp;cpu_sibling_map[cpu]` en MIPS). Un poco de depuración me llevó a que set_cpu_sibling_map() realizaba el cálculo del mapa real, se invocaba después de notify_cpu_start(), y exactamente la última función inicia la ronda de devolución de llamada de CPU HP (sched_core_cpu_starting() es básicamente una devolución de llamada de CPU HP). Si bien el flujo es el mismo en ARM64 (mapas después del notificador, aunque antes de llamar a set_cpu_online()), x86 comenzó a calcular mapas de hermanos antes de iniciar las devoluciones de llamada de CPU HP en Linux 4.14 (consulte [0] para la referencia). Ni yo ni mis breves pruebas pudimos encontrar posibles advertencias al calcular los mapas justo después de realizar la calibración de retraso, pero el símbolo WARN ya no está. Las mismas impresiones de depuración ahora producen exactamente lo que esperaba de ellas: [0.048433] CPU: 1, smt_mask: 0-1 [0] https://git.kernel.org/pub/scm/linux/kernel/git/mips /linux.git/commit/?id=76ce7cfe35ef

*Credits: N/A
CVSS Scores
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-07-16 CVE Reserved
  • 2024-07-16 CVE Published
  • 2024-07-25 EPSS Updated
  • 2024-11-04 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 4.9.308
Search vendor "Linux" for product "Linux Kernel" and version " < 4.9.308"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 4.14.273
Search vendor "Linux" for product "Linux Kernel" and version " < 4.14.273"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 4.19.236
Search vendor "Linux" for product "Linux Kernel" and version " < 4.19.236"
en
Affected
Linux
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Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 5.4.186
Search vendor "Linux" for product "Linux Kernel" and version " < 5.4.186"
en
Affected
Linux
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Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 5.10.107
Search vendor "Linux" for product "Linux Kernel" and version " < 5.10.107"
en
Affected
Linux
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Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 5.15.30
Search vendor "Linux" for product "Linux Kernel" and version " < 5.15.30"
en
Affected
Linux
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Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
< 5.16.16
Search vendor "Linux" for product "Linux Kernel" and version " < 5.16.16"
en
Affected
Linux
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Linux Kernel
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< 5.17
Search vendor "Linux" for product "Linux Kernel" and version " < 5.17"
en
Affected